1. Field of the Invention
Aspects of the present invention relates to a battery charging apparatus, and more particularly, to a battery charging apparatus, a battery pack, a battery charging system, and a battery charging method.
2. Description of the Related Art
Rechargeable (secondary) batteries have been actively studied for use in mobile electronic devices, for example, mobile phones, notebook computers, camcorders, and Personal Digital Assistants (PDAs).
The most commonly used rechargeable batteries are Lithium Ion batteries, Lithium Ion Polymer batteries, Nickel-Cadmium batteries, Nickel Metal Hydride batteries, and the like. Among these, Lithium Ion batteries and Lithium Ion Polymer batteries, which are used for notebook computers, have many advantages, such as, a high energy density, a high operating voltage, good conservation characteristics, and a long service life. However, due to safety problems, it is difficult to manufacture Lithium Ion and Lithium Ion Polymer batteries having a high enough power, to enable a high current flow.
FIG. 1 is a block diagram illustrating a conventional battery charging apparatus and a battery pack. Referring to FIG. 1, an AC/DC converter 102 converts an AC voltage supplied from a voltage receptacle into a DC voltage and transmits the converted DC voltage to a charger 104.
The charger 104 controls the charging of a battery pack 106. When the charger 104 is used for charging a Lithium Ion Polymer battery pack, the charger 104 employs a constant current/constant voltage method or a pulse charging method. These methods are relatively safer charging methods, as compared to a method for charging a Nickel-Cadmium battery or a Nickel Metal Hydride battery. In the case of the Lithium Ion Polymer battery pack, a basic voltage and a charging voltage, per a battery cell, are 3.7 volts and 4.2 volts, respectively, and a charging current is generally less than 1 Coulomb (C).
The battery pack 106 includes a Protection Control Module (PCM) 108 and a plurality of battery cells 110, 112, and 114. The battery pack 106 includes the PCM 108 to prevent an overcharge or an overdischarge of a Lithium Ion battery or a Lithium Ion Polymer battery, due to safety problems. Current from the PCM 108 is equally applied to all of the battery cells 110, 112, and 114, when charging the battery pack 106.
FIG. 2 shows a graph of a battery charging process performed by the battery charging apparatus of FIG. 1, using a conventional constant current/constant voltage method. Referring to FIG. 2, the charger 104 regularly applies a maximum charging current IMAX to the battery pack 106. Then, a voltage 204 of the battery pack 106 is increased gradually up to a charging voltage VREG (defined as a “constant current” state). When the voltage 204 of the battery pack 106 reaches the charging voltage VREG, the voltage 204 is maintained and then a current 202 is gradually decreased (defined as a “constant voltage” state). When the current 202 decreases to a minimum current IMIN, the charging is ended.
In order to reduce the time required for fully charging a battery, the maximum charging current IMAX should be increased. However, increasing the maximum charging current IMAX can reduce the performance of a battery.
FIG. 3 shows a graph of a battery charging process performed by a battery charging apparatus, using a conventional pulse charging method. Referring to FIG. 3, to solve the aforementioned problem, a pulse current 302, which includes a plurality of charge pulses, is used in the pulse charging. The pulse current 302 can protect battery performance and reduce the time required for charging. In the conventional pulse charging method, a battery voltage 304 is detected, charging is stopped when the battery voltage 304 reaches a voltage V1, and charging is resumed when the battery voltage 304 declines to a voltage V2.
However, in a Lithium Ion Polymer battery pack having 3 battery cells connected in parallel and each having a capacity of 1000 mAh, the charging time increases due to a limitation on the charging current needed by the battery cell. Also, when a plurality of battery cells are connected in parallel, a battery charging capacity should be determined considering a capacity of a charger. In this case, a charging time of at least 5 hours is required, due to the charging current limitations of each battery cell. Therefore, the battery charging time, which increases in proportion to an increase of battery capacity, should be reduced.